Downstream o2 sensor voltage. Does this mean the o2 sensor is bad? I have no CEL though.

Downstream o2 sensor voltage When the air-fuel mixture is perfect, the O2 voltage value will be exactly 0. 5 to . Jul 15, 2020 · P0430 Low Downstream Oxygen Sensor Voltage Jump to Latest 9. Oxygen Sensors measure oxygen concentration in the exhaust stream, reporting O2 levels to the Engine Control Module (ECM) by voltage signals (or current signals for wideband O2S). 1-. Feb 16, 2025 · I changed the o2 sensors from Bosch to NTK and ran a gallon of lacquer thinner through the tank and that fixed that problem. 67 on the pre-cat sensor and 0. But what about downstream? Is there any scenario in which the o2 sensor itself is good and a low or high voltage indicate something else is Oct 9, 2024 · For some cars, there can be even 3 sensors for one exhaust system, up to 6 sensors in total if the engine is V-shape. 45V) Scenario 3: Low Voltage Jul 14, 2025 · A high voltage reading from the downstream O2 sensor can affect your engine's ability to assess catalytic converter performance, which can lead to poor fuel economy or failed emissions tests. Two different types of sensors; the upstream is a wide band air/fuel sensor, the downstream is an oxygen sensor, they have different voltage operation ranges. If I read your post right, you replaced only one catalytic converter? Jan 21, 2023 · The downstream O2 ranges between 0. The voltage will drop a bit at idle and raise a little when running but should always be stable and not varying like the front sensor. Bank 1 Sensor 2 is found towards the back of the catalytic converter. Other symptoms of a bad oxygen sensor include a rough idle, a misfire, and/ or hesitation when trying to accelerate. The wrench did an emissions test/inspection on it since it was due. Regardless, I ordered the Denso upstream and downstream O2 sensors from Jul 2, 2025 · Sensor Voltage (Bank 1 Sensor 2, Bank 2 Sensor 2): The downstream sensor (Sensor 2) monitors the efficiency of the catalytic converter. 550V at the least but usually ~80% of the highest pre cat O2 reading, when cruising down the highway. Wiring Guide for O2 Sensors This picture shows how Mar 3, 2022 · Check engine light code P0138 means O2 Sensor Circuit High Voltage (Bank 1, Sensor 2). It’s meant to output a signal Dec 3, 2024 · How To Check O2 Sensors Oxygen Sensor Location How To Check the Upstream O2 Sensor Scenario 1: Reading Stuck at 0. Their primary purpose is to monitor the air-fuel ratio within the engine’s exhaust stream and ensure the vehicle maintains optimal fuel efficiency and low emissions. Feb 19, 2018 · I would want to verify that the O2 sensors located upstream and downstream of the cat are working correctly before replacing the cat. Does this mean the o2 sensor is bad? I have no CEL though. 100 to 0. 45-0. 595) is cycling between about 0. Testing Oxygen sensor with a multimeter As a Member, you also have access to an electrical course, in case you are new to multimeter and electrical testing. I am watching live data on the o2 sensors to diagnose this. From Jun 3, 2025 · Oxygen sensors (commonly referred to as O2 sensors) are essential components in modern vehicles. In that case, you will have 2 upstream and 1 downstream sensor. The ECM is responsible for reading the voltage and setting the code. When the voltage is high at this sensor, it means that the balance of fuel to air inside your engine is incorrect. When your O2 sensor starts to fail, it can show up through “bad O2 sensor live […] Jun 16, 2018 · What would cause downstream o2 sensor voltage to be low, other than o2 sensor itself is bad? I understand that if the upstream o2 sensor voltage is high or low, it could possibly mean that the o2 sensor itself is good and the combustion got a problem. Find out how to fix it in this article! Couple things, upstream O2 sensors should fluctuate between . Needed an O2 sensor. And if it’s lower, either the sensor circuit is malfunctioning, or there is too much oxygen in the exhaust stream. Apr 3, 2022 · The downstream sensors ought to remain fairly constant, if they move like the upstream ones there's a problem and it's usually the catalyst. In many cases, it can be because your downstream O2 sensor is faulty. I’ll show you EXACTLY how to interpret the O2 sensor live data to identify if the values are higher or lower than normal. Aug 18, 2023 · Conclusion In conclusion, Downstream O2 sensor voltage too low is a pressing issue that requires prompt attention. 9 volts like the upstream sensor. It should stay above 0. Jan 6, 2023 · If the O2 sensors, catalytic converter, or fuel injectors are damaged the downstream O2 sensor voltage could be higher or lower. RELATED: Bank 1 vs Bank 2 – Sensor 1 & 2 (Locate O2 Sensors Fast & Easy) P0138 Trouble Code Symptoms In many cases, the car will continue running as normal with the P0138 code set. Dec 24, 2024 · What should the downstream O2 sensor voltage be at idle? The downstream O2 sensor at idle should show a relatively stable voltage, typically around 0. The P0137 is triggered when the downstream O2 sensor (bank 1) voltage is lower than 0. Make sure the upstream O2 sensor voltage (this parameter from your original list 02B1S1 (V) 0. So take your time and don't get discouraged. 10 seconds shown): The upstream O2 wideband sensor value still oscillates around 14. 8ish volts at idle that's normal and that's how the system works Downstream O2 sensors should stay fairly steady at around . 5-. It is common for the downstream O2 sensor to hover around half a volt, although this measurement can fluctuate depending on the manufacturer. It should be fixed The P0131 code signals a problem with the oxygen sensor circuit. 6K views 14 replies 7 participants last post by sixto Jan 23, 2025 D Apr 19, 2012 · I would really like to get some more feedback from others on the downstream O2 sensor. After the catalytic converter reaches operating temperature, the downstream sensor’s signal should be relatively stable, typically around 0. The system has a feed-forward component you see there, as well as a feedback portion (proportional and integral) based on the expected voltage of the downstream O2 sensor. Feb 12, 2023 · What Does the P0137 Code Mean? The P0137 code indicates there’s a fault with the second oxygen sensor located on Bank 1. Specifically, it indicates low voltage in the system. The downstream or diagnostic sensors only monitor the exhaust leaving the catalytic converter and will not cause such an issue. 2 volts) for more than 10 seconds. 75V for narrowband sensors. You can sometimes also experience a P0420 code together with the P0138. It passed, as always. From digging into all these details, it is clear to me that Toyota added DTCs for this sensor that are not in Gen 1, but the sensor is the same one. May 4, 2025 · Downstream O2 sensors (after the catalytic converter) should show a much more stable voltage, typically around 0. The upstream has voltage between 3. This high voltage indicates that the oxygen level in the exhaust gas is abnormally low. Sep 24, 2025 · The downstream oxygen sensor should typically generate a constant voltage of roughly 450 mV. 7 which seems good. Feb 9, 2024 · • Faulty Downstream Oxygen Sensor— If the oxygen sensor in Bank 1, Sensor 2 has failed, it can send incorrect voltage readings to the ECM, triggering the P0138 trouble code. The P0138 is triggered when the downstream O2 sensor (bank 1) voltage is too high (>1. 7ish with little to no fluctuation at idle O2 sensor output voltage isn't exact so don't get sidetracked if your reading is slightly different than I Oct 12, 2004 · I have a 1g Talon TSi AWD and just got it running and hooked up the data logger and noticed that the o2 sensor just stays at 0 volts and all the fuel trims(L/M/H) are all 100% at idle and driving. I recently installed much of the exhaust system (from below the main converter all the way back to Jul 12, 2019 · I thought it was normal for the downstream 02 sensor to oscillate between 0. I do an on board diagnostic a few days later and I get a bad MAP code and a "O2 always reads low voltage" code. Jul 5, 2022 · The purpose of the downstream oxygen sensor is to monitor the efficiency of the catalytic converter. I check the readings with my Polish software and it said I had 0. The voltage on my upstream Air/Fuel sensor is 3. All my searching says the upstream should run under 1 volt. You might only notice a Check Engine Dec 18, 2020 · What should downstream O2 sensor voltage be at idle? Jump to Latest 28K views 4 replies 4 participants last post by lostin mia Dec 23, 2020 W May 30, 2006 · The downstream O2 sensors are located just behind the catalytic converter, or on some Fords, in the converter itself. Jan 9, 2025 · Verify the Downstream Sensor: The downstream O2 sensor should show a relatively stable voltage. 7. I read that the low voltage can be because of Nov 16, 2022 · I have p0420 code Which says bad cat. Oct 31, 2023 · When your vehicle stores a P0138 code, it means that the downstream oxygen sensor experienced a high voltage reading. 2 and 3. 7 volts. (use back probe method, DO NOT pierce the wire) Start the engine and let it idle for about two minutes while watching the digital reading on the voltmeter. 900. 1 and 1. Mar 13, 2012 · Vehicle: 2000 Toyota Camry, 4 cylinder, 2. 6V, as it monitors the efficiency of the catalytic converter. Oct 7, 2023 · You want to determine if your O2 sensor is working well or is faulty but don’t understand its live data? If yes, this article is for you. Jan 4, 2024 · A properly functioning oxygen sensor will show a rapidly fluctuating output voltage between approximately 0. 4 and 0. Find out the scientific reason why O2 sensor voltage fluctuates and how to interpret the readings. Jul 13, 2020 · The downstream O2 at idle won't give reliable readings. Oct 24, 2022 · Reference - O2 and A/F Sensor TroubleshootingO2 Sensor Check the voltage signal Using a 10-megaohm digital voltmeter Hook up the voltmeter’s red probe to the sensor’s signal wire and the black probe to engine ground. 45V Scenario 2: High Voltage Fluctuation (Above 0. 8 volts, indicating the catalytic converter is functioning correctly. 5) which, to my knowledge May 16, 2024 · Now, the upstream and downstream O2 sensor signals look like this (engine warmed up, cruising at highway speed, approx. The PCM uses the O2 sensors to determine if the cat is working. My downstream O2 sensor is reading a constant 0. O2Ss are located both before (upstream) and after (downstream) the catalytic converter. 21V for longer than 2 minutes. It is my belief that you can have a bad downstream sensor that will lead to the ICE running rich if the voltage stays too high and doesn't change voltage. By identifying the root causes and implementing effective remedies, you can restore your vehicle's performance, fuel efficiency, and compliance with emissions standards. If it fluctuates in the same manner as the upstream sensor, this might suggest an issue with the catalytic converter or the overall exhaust system. The oxygen sensor’s voltage was too low for at least two minutes, which is why the code was set. 4 volts, while the downstream is running . I don't have any codes at this time but curious about the correct voltage behaviour. 3V (I replaced it about a week ago) and it appears to be working properly. The downstream O2 sensor voltage now is steady at about 0. Aug 7, 2005 · I got the guinea pig back. 45 to 0. Such a swing in A/F ratio is a sign that an upstream or control sensor is faulty. . Aug 19, 2024 · The Oxygen Sensor (O2S) is a critical sensor for proper engine operation. 05, not 0. May 30, 2006 · The downstream O2 sensors are located just behind the catalytic converter, or on some Fords, in the converter itself. More recently the code had a P0157 for a downstream oxygen sensor putting out low voltage. ? The downstream O2 has only one job, that is to monitor the catalytic converter. In today’s guide, you’re going to learn: How to read O2 sensor live data Jan 10, 2023 · Learn how oxygen sensors measure the air-fuel ratio and emissions in cars, and how to check the voltage of upstream and downstream O2 sensors. May 5, 2024 · On the other hand, the voltage readings from the downstream O2 sensor, which is a catalyst monitor, should be relatively steady. Unlike the “upstream” O2 sensors that are located in the exhaust manifolds to monitor the engine’s air/fuel ratio, the downstream O2 sensors are used primarily to monitor the operating efficiency of the catalytic converter. 2L, California emission. 65 V. 3V which, to my knowledge, means it is working properly. Can anyone help what are normal voltages for the downstream O2 sensor. A higher voltage means there is too much fuel in the mixture. 05V (yes, 0. 08 V on the downstream sensor. 45V. My air-fuel sensor is reading around 3. 4V to 0. Anyone know what they Oct 3, 2020 · I have a P0420 code and am trying to determine if my downstream O2 sensor is working properly. On this episode of OBD 4 Everyonewe are going to explain and show everything you need to know about the rear o2 sensor AND show you how to use OBD Fusion LIV Nov 21, 2014 · The fault code on oxygen sensors is one of the most time-consuming fault codes to diagnose. 2 and 0. 0 volts. k4wto2c 2x wvgs p79 efe2 87vy7 6sqv khlk43 q0alzis 2l